Overview

Angiosperms or flowering plants comprise the largest group of all modern plants.  They are vascular and seed bearing, with the seed being covered.  Angiosperms dominate the land plants, with roughly 90 percent of all species.  They diverged from gymnosperms 200-230 million years with the introduction of the protected seed and have further diverged into monocots and dicots. Derived from the Greek word Angion meaning container and sperm meaning seed, literally translated to covered seed.   

Evolution

Angiosperms have evolved to produce both protected seeds and flowers.  The flowers allow for pollination to be less wind reliant, by allowing animals such as bees and hummingbirds to take pollen to the ovules of either the same or different plant.  Flowers themselves are highly evolved so they attract animals with a sweet scent and vibrant coloration, this insures pollination.  Most seeds of angiosperms have adaptations to better disperse seeds.  These include propeller like seeds of certain trees and the fruits of other plants.  These fruits are mature ovaries that are very charming to the palette and incredibly nutritious, once excreted, the seeds can be miles away from the parent plant with a source of fertilization effectively spreading the species.   

Structure

There is a distinct hierarchy of cells, tissues, and organs seen in plants.  The 3 basic organs are the roots, stems and leaves 

      Roots

This organ roots the plant firmly in the ground and also uptakes minerals and water, as well as storing nutrients.  They are lengthend by meristems and include a root cap to protect the root and lubricate the soil for penetration. 

Root systems are broken down in two types

• Taproots
  • most commonly found in gymnosperms and dicots
  • a large vertical root with smaller branching roots
  • usually is deep in the ground
• Fibrous root system
  • Found in monocots and seedless vascular plants
  • many lateral roots  bundled together for an increase in surface area 
  • usually more shallow than taproots
• Roots can be modified by adaption to include above ground roots
  • Prop roots-roots above ground
  • Storage roots- stores nutrients
  • Aerial roots
  • buttress roots- for support
  • pneumatophores-air roots, for mangroves

     Stems

The stem is the plant organ between the leaves and roots of the plant.  It consists of an alternating system of nodes and internodes.

Stems can be modified to include

• bulbs- underground shoots made of an enlarged base of leaves
• tubers-food storage
• Stolons-horizontal stems
• Rhizomes- a horizontal underground stem

     Leaves

These are the main photosynthetic organ of the plant they can either be simple or compound, which just is the amount of leaves per bud.  Some leaves have been modified to include tendrils, spines, storage, bracts, and reproductive parts

     Tissue 

Plants are made up of several tissue types, the three systems known as dermal, vascular, and ground tissue.  The dermal tissue covers the entire plant, while the ground tissue performs most of the plants metabolic functions, and the innermost vascular tissue conducts sugar and water across the plant.  Plants have three different cell types 

• Parenchyma-thin and flexible cells 
• Collenchyma cells- the glue of the plant 
• Sclernchyma cells- the hard outer cells strengthend by lignin, usually are dead cells            

There are two types of vascular tissue: 

• Xylem- runs water from the roots to the top of the plant 
• Pholem-runs sugar from the leaves of the plant to the roots  

This vascular tissue is arranged in a ring in dicots and scattered randomly in monocots 

Woody tissue, found in some angiosperms, is the result of secondary growth of phloem and xylem 

     Flowers 

All angiosperms have flowers most flowers, although different in appearance and adaptation,  

have similar basic structure including 

• --Brightly colored petals to attract potential pollinators 
• --A stamen consisting of an anther and connecting filament 
• --the carpel consisting of stigma, style, and ovary                                                                           
• --the repetical and ovary 
• --^[1][2]the sepal- left over covering of the pre blooming bud   

 Life Cycle

The Angiosperm life cycle is centered in its evolved reproductive organ of the flower.  Anthers contain microsporangia, each containing microsporocytes that divide through meiosis producing male microspores to form pollen grains. The pollen grain then enters the stigma through the pollen tube and into an ovule, which at the same time is dividing by meiosis into four megaspores, the surviving one becoming the female gametophyte.  The sperm then fertilizes the egg through a pollen tube.  The zygote is immersed in the nutritive fluid known as endosperm.  The zygote divides mitiotically and eventually germinates into a seedling of a mature sporophyte. 

Uses

• Medicine 
  • as much a 80 percent of medicine is derived from angiosperms  
• Lumber 
  • many angiosperms are woody plants 
• Major food staple throughout human history 
• Beverages   

Gymnosperms